This study was designed to determine the significance of the large changes in renin substrate, aldosterone, and blood volume in pregnancy. The role of the renin angiotensin system on uterine function will also be examined. The mechanisms responsible for the blocking of the biological effects of aldosterone in pregnancy will be studied. The study was also designed to examine the mechanisms responsible for the decrease in blood pressure during pregnancy in renal hypertensive and spontaneous hypertensive animals; specifically the blood pressure lowering effect of various hormones of pregnancy. The basic comparison will be that of the difference in blood pressure found between the pregnant animals and their nonpregnant controls and will be analyzed by standard techniques. BIBLIOGRAPHIC REFERENCES: Parks, Burce R., G.H. Douglas, and John R. Rawson. The effect of maternal lithium (Li) ingestion on blood levels of Li in suckling subhuman primates. J. Miss. Acad. Sci., Vol. 22, 1976. Douglas, Ben H. The rat as a model for preeclampsia. In: Hypertension During Pregnancy (ed. M.D. Lindheimer). John Wiley & Sons, Inc., publisher, New York, 1976, in press.